near field communicatin

8/2/2019 Near Field Communicatin

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Near-Field CommunicationGroup #31

Keshav Bansal

Dan HvalaTyler Rossi


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Introduction NFC is a short-range wireless

technology.

NFC provides unique advantages overother available wireless technologies.

The design includes a near-field

transmitter and receiver to send datafrom one computer to another


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Benefits & Features Not restricted to 1-to-1 communication

Multiple devices in a small area can

communicate with each other using thesame frequency.

Maximum transfer bit rate of 800kbps.

No special software is required. Operation at a frequency of 13.5 MHz

No ethical concerns due to range


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Modulation/Demodulation

Scheme Frequency Shift Keying (FSK)

VCO produces a frequency-modulated

signal at the transmitter

Phase lock loop demodulates the signal atthe receiver.


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System Overview Hardware

Transmitter

PC interface (MAX232A) Voltage-Controlled Oscillator (POS+25)

Power Amplifier (LM6181)

Loop Antenna

Receiver Loop Antenna

Amplifier (LM6181)

Phase Lock Loop (NE564)

PC interface (MAX232A)


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System Overview


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Pictures


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System Overview(Schematic)

5

4

3

2

1

9

7

6

8

Serial Port

VCC

0.1uF

0.1uF

0.1uF

0.1uF

0.1uF

1

2

3

4

8

7

6

5

16

15

14

13

9

10

11

12

MAX232A

T1 Out

C2+

C1+

T1 InV-

C2-

V+ Gnd

VCC

R1 In

T2 InT2 Out

C1-

R2 OutR2 In

R1 Out

Antenna

50

50

50

820820

V+

V-

LM6181

8

7

6

5

1

2

3

4

POS

-25VCO

VTune

GND

RFOut

VCC

GND

GND

GND

GND

2K

220

180

180

180180

V-

V+

HA17741

3.7V

Antenna

VCC

0.1uF

0.1uF

0.1uF

0.1uF

0.1uF

1

2

3

4

8

7

6

5

1

61514

13

9

10

11

12

MAX232A

T1 Out

C2+

C1+

T1 InV-

C2-

V+ Gnd

VCC

R1 In

T2 InT2 Out

C1-

R2 OutR2 In

R1 Out

1

2

3

4

8

7

6

5

161514

13

9

10

11

12

NE564

AnalogueOut

Loop Filter

V+

VCOOutFM/RF Input

Loop Filter

LoopGain

Control

Hysteresis

set

TTLOutput

Set Cap

V+Bias Filter

Input

VCOOutTTL

Ground

Set Cap

5

4

3

2

1

9

7

6

8

Serial Port

50

50

50

820820

V+

V-

1K

1K

2K

1.2K

10K

5V

5V

300pF

300pF

0.1uF

0.1uF

510

510

33pF

10uF

0.22uF0.22uF

10K


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PC Interface Connects through serial cable

Received by MAX232A

0 to 5V square wave

Voltage divider

Non-inverting voltage adder


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PC Interface

(Schematic)

5

4

3

2

1

9

7

6

8

Serial Port

VCC

0.1uF

0.1uF

0.1uF

0.1uF

0.1uF

1

2

3

4

8

7

6

5

16

15

14

13

9

10

11

12

MAX232A

T1 Out

C2+

C1+

T1 InV-

C2-

V+ Gnd

VCC

R1 In

T2 InT2 Out

C1-

R2 OutR2 In

R1 Out

2K

220

180

180

180180

V-

V+

HA17741

3.7V


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MAX232A Input/Output


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Voltage Controlled Oscillator Operates on a 12-V power supply

Accepts an input from 3.7V to 4.2V

from the PC interface. Outputs a signal whose frequency

varies according to the input voltage

level


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VCO Output


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Power AmplifierAccepts an input from the VCO

Outputs the signal to the loop antenna

Power gain of approximately 11dB


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Power Amplifier

(Schematic)

50

50

50

820820

V+

V-

Vin

Vout


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Amplifier Input/Output


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Loop Antenna

Loop Diameter = 6.5 cm

Inductance = 3 uH

Capacitor used to resonate the antennaat 13.5 MHz = 45 pF


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Loop Antenna

Very directional

Larger loop = more gain

Picks up less noise

Small, multi-loop turn does not radiatemuch


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Frequency Comparisons


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Phase Lock Loop

Tracks the frequency and phase of theinput

Frequency of an FSK signal changesaccording to the data bits; therefore,PLL can demodulate an FSK signal.

Output is the VCO control voltage.


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Phase Lock Loop(Block Diagram)


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Phase Lock Loop Tracking


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Band-Pass Filters(Eliminated)

Tuned to 10MHz and 13.5MHz

Pass-band of 2-3MHz

Signal did not decay fast enough outside ofthe pass-band

Vin

-

+Vout

+Supply

-Supply


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Difficulties

Small antenna bandwidth made us torevise our original design.

Drift in the frequency of VCO.

Amplifier oscillation

Most significant bit flipping


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Future Hardware Development

Less power consumption

More efficient loop antenna for larger

range.

Smaller setup

Two-way communication


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Analysis

Strengths

No interference due to decaying fields

Within FCC regulation FCC requires max E-field of 334uV/m at 30m

Our max E-field at 30m is 180uV/m

Weaknesses

Very small range Sensitive to distance and alignment

653mW


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Results

Maximum bit rate of 800kbps

Text communication between two PCs

Transmission range of 30cm

Ability to send a text file between PCs


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Credits

Ethan Miller

Dr. Ada Y. Poon

Dr. Christopher Schmitz

Dr. Steven Franke

Workers in the ECE Parts Shop

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